Multiple photocells and method of making same



Nov. 15, 1960 F. P. STROTHER MULTIPLE PHOTOCELLS AND METHOD OF MAKING SAME 2 Sheets-Sheet 1 P5 4 T k 7% v w m ml i 7 3 Mm K km a M 2 fi NZ W M s w 0 H00 SS. 00f E H R W V M Z; 3 F M M G M m w# m m m C n O F w Mu BY 3 D {M TTORNEYS Nov. 15, 1960 F. P. STROTHER 2,960,417

MULTIPLE PHOTOCELLS AND Mz'raon OF MAKING SAME Filed July 23, 1958 2 Sheets-Sheet 2 ATTORNEYS United States Patent MULTIPLE PHOTOCELLS AND LIETHOD OF MAKING SAME Fred P. Strother, Shawmut, Ala., assignor to West Point Manufacturing Company, West Point, Ga., a corporation of Georgia Filed July 23, 1958, Ser. No. 750,496

7 Claims. (Cl. 117-212) The present invention relates to photocells and novel :methods of making same.

The principal object of the invention is the provision 0f multiple photocells of relatively small size suitable .for use in automation, data reduction, process control, :and the like where operation or control by means of a :number of closely spaced photocells may be desirable.

.Another object of the invention is to provide a compact photocell unit made up of a substantial number of closely spaced photocells. A further object includes the provision of a unique and relatively easy method of preparing multiple photocells of the type referred to above. Another object of the invention is the provision of novel means for connecting to the cells. Other objects will also be apparent from the following detailed description of the invention.

Broadly stated, the method of preparing multiple photocells according to the present invention involves the steps of applying a relatively wide strip coating of photo sensitive material along the length of a threaded, or otherwise transversely grooved, dielectric rod or the like; then masking a longitudinal strip of the coating somewhat narrower than the Wide strip of photosensitive material and applying a metallic conductive overcoating on the photosensitive coating while maintaining the masked strip; then removing the mask and masking the grooves 'Figure 7 illustrates the removal of the mask and the metallic coating above it;

Figure 8 is a section taken along lines 88 of Figure 7' Figure 9 illustrates the masking of the grooves of the rod;

Figure 10 is a section taken along lines 10-10 of Figure 9;

Figure 11 shows the removal of the coatings on the raised positions of the rod;

Figure 12 is a section taken along lines 12-12 of Figure 11;

Figure 13 shows the finished photocell;

Figure 14 is a section taken along lines 1414 of Figure 13;

Figure 15 is a front view looking toward the photocell and showing electrical contact with the photocell;

Figure 16 is a plan view corresponding to Figure 15 and;

Figure 17 is a section along lines 1717 of Figure 16;

Referring more specifically to the drawings, a threaded, or otherwise annularly grooved, rod 2 of suitable dielectric material, e.g., a ceramic such as porcelain, is coated on one side, in the manner shown in Figures 1 and 2, with a relatively wide strip of cadmium selenide, cadmium sulfide or other photosensitive material 4. The material may be applied to rod 2 in any conventional fashion, e.g., by aqueous suspension, evaporation, silk screen, etc. The coated rod is then suitably treated, e.g., heated at sufficiently high temperature to sinter the photosensitive material. The material may be sensitized at this point also by any of several known methods, e.g.,

of the rod, preferably by winding a round rubber core or the like about the rod, followed by sandblasting or otherwise removing all of the metallic overcoating and photosensitive coating on the rod except for that masked in the grooves and then removing the mask from the grooves.

The present method, as briefly described above, gives a highly useful photocell unit comprising a plurality of small photocells positioned in the bottom of the grooves of the rod. It will be appreciated that the method makes it possible to provide a photocell unit having a large number of photocells over a small unit of length, the relative distance between the cells being dependent upon the spacing of the threads or grooves in the rod. Typically, it is possible to provide as many as 32 photocells, or even 60-70 cells or more, per inch of rod length by means of the instant invention.

The invention will be more fully understood by reference to the following detailed description thereof in connection with the accompanying drawings wherein:

Figures 1 to 14 illustrate the various steps of the process and more specifically:

Figure 1 shows the rod coated with photosensitive material;

Figure 2 is a section taken along lines 2-2 of Figure 1;

Figure 3 shows the masking of a narrow strip of photosensitive material;

Figure 4- is a section taken along lines 44 of Figure 3;

Figure 5 shows the metal overcoated rod;

Figure 6 is a section taken along lines 6-6 of Figure 5;

with halogens and copper salts. A relatively narrower strip of the photosensitive coating is then masked over the entire length of the coating. This may be done in a variety of ways, as for example by applying a removable tape or masking strip 5 as shown in Figures 3 and 4 along the length of the coating. In a preferred method, the masking is accomplished by placing the rod in a jig in such a way as to cover a longitudinal strip of the photosensitive coating. In any case, after the strip of coating 4 is masked, a layer '6 of conductive metal such as gold, silver, indium, etc., is applied over all of the coating 4, as shown in Figures 5 and 6, except for that covered by the mask. This coating of metal, preferably gold, may be applied in any convenient manner, e.g., by painting, dipping, spraying or the like. Preferably, however, the metal is applied by evaporation in a high vacuum. Ths insures a uniform conductive metal overcoating on all of the photosensitive surface except that covered by the jig or otherwise masked. The gold or other metal overcoating may be applied only on that portion of the rod that has been coated with material 4. As an alternative, the overcoating may be extended beyond the photosensitive material 4 to facilitate connecting the cells, as described hereinafter.

Following the application of the metal overcoating, the strip mask 5 is removed together with the portion of the conductive metal coating above the strip 5, leaving the longitudinal strip of photosensitive material 4 shown in Figure 2, As will be appreciated, the application of metal coating 6 in the manner described above effectively forms a photocell extending the full length of the rod with a relatively short distance, i.e. the width of the masked strip, separating the electrodes.

The bottom portion of the grooves of rod 2 are then masked, preferably by winding a round rubber cord 8 or the like under constant tension, into the threads or grooves in the manner shown in Figures 9 and 10. The size of the rubber cord or other masking means 8 should be chosen to fit within the grooves and effectively mask the metallic overcoating 6 and photosensitive layer 4 in the bottom part of the grooves. The amount of masking can be regulated by the tension of the rubber during the winding operations. Typically suitable winding tensions maybe, for example, 4 to 6 oz. for rubber cord in diameter.

The thus-masked rod is then sandblasted, or otherwise treated as shown in Figures 11 and 12, to remove all of the photosensitive material and conductive metal overcoating not masked by masking means 8 and lying on the raised portion of the treated rod 2. The masking means 8 are then removed from the rod to leave a series of individual photocells, i.e. one photocell in the bottom of each groove, along the full length of the threaded rod. Each of these photocells as shown in Figures 13 and 14 comprises spaced electrode portions formed by the metallic overcoating 6 with the exposed photosensitive layer 4 therebetween.

If desired, all of the cells may be provided with a common connection along one side of the assembly. This may be accomplished by, for example, the application of silver paint or other suitable conducting means connecting all of the cells along one side.

Figures 15 to 17 also show a preferred arrangement for making contact with individual cells. The arrangement, as illustrated, includes a wire comb made up of a series of highly conductive spring wires 10, typically beryllium/ copper wire having a silver overcoat, embedded in a block 12, of suitable non-conducting plastic such as polymethylmethacrylate or the like. Each of the wires is adapted to rest in the bottom of a groove for contact with one of the electrodes 6 of the photocell. Such contact is preferably completed by means of additional conductive metal, e.g., silver paint, representing an extension 14 for each electrode. This extension may be provided for during the overcoating operation, as in! dicated heretofore, or by the application of silver paint or the like after the overcoating. Subsequent sandblasting removes all of such additional metal except for the masked extensions in the bottom of the grooves. As a further alternative, the extension may be formed by suitably painting the grooves with silver or the like after the sandblasting operation.

As shown, the opposite free ends of the wires are so formed as to permit making connections with auxiliary equipment. It will be recognized that this arrangement makes it possible to have individual contacts for practically any number of photocells, regardless of how closely spaced the cells may be, since the free ends of wires 10 can be bent or deformed as desired to make whatever auxiliary connections are necessary.

It is particularly desirable in practicing the method described herein to subject the rod coated with photosensitive material to ionic bombardment prior to application of the overcoating metal. Typically, such bombardment may be carried out for a period of about 30 seconds to 2 minutes using a pressure of the order of 1 mm. of mercury. Other conditions normally employed in carrying out ionic bombardment may also be used. Such bombardment allows considerable control and modification of the final electrical characteristics of the photocells described herein. For instance, it has been found that ionic bombardment reduces the light-on resistance of the photocells by a factor of 10 over the untreated cells and does not seriously affect the dark resistance.

It will be appreciated that the photocells described herein have a variety of uses. Typically, the present photocell units are useful in the textile industry for the purpose of regulating or controlling the feed of fabric undergoing treatment. It will also be understood that various modifications may be made in the invention described herein without deviating from the scope thereof as set forth in the following claims, wherein:

I claim:

1. The method of preparing multiple photocells which comprises the steps of applying a wide longitudinally-extending strip of photosensitive coating along the length of a dielectric rod having a series of transverse grooves therein; masking a longitudinal strip of said coating with a first mask narrower than said wide strip, thereafter applying a metallic conductive overcoating on said photosensitive coating while maintaining said masked strip; removing said first mask and masking said transverse grooves with a second mask while leaving the ridges between grooves exposed; then removing the metallic overcoating and photosensitive material from the portions of said rod which remain exposed, and thereafter removing the second mask from said transverse grooves.

2. The method of claim 1 wherein said rod is a threaded ceramic rod.

3. The method of claim 1 wherein said photosensitive coating includes selenium.

4. The method of claim 1 wherein said second mask is a round rubber cord under essentially constant tension.

5. The method of claim 1 wherein said metallic overcoating and photosensitive coating are removed by sandblasting.

6. The method of claim 1 wherein said rod is subjected to ionic bombardment prior to application of said overcoating.

7. The method of claim 6 wherein said bombardment is effected over a period between about 30 seconds to 2 minutes at a pressure of about 1 mm. mercury.

References Cited in the file of this patent UNITED STATES PATENTS 1,303,404 Simon May 13, 1919 2,781,282 Morgan et al. Feb. 12, 1957 2,813,957 Gosling Nov. 19, 1957 2,839,646 Hester June 17, 1958 

1. THE METHOD OF PREPARING MULTIPLE PHOTOCELLS WHICH COMPRISES THE STEPS OF APPLYING A WIDE LONGITUDINALLY-EXTENDING STRIP OF PHOTOSENSITIVE COATING ALONG THE LENGTH OF A DIELECTRIC ROD HAVING A SERIES OF TRANSVERSE GROOVES THEREIN, MASKING A LONGITUDINAL STRIP OF SAID COATING WITH A FIRST MASK NARROWER THAN SAID WIDE STRIP, THEREAFTER APPLYING A METALLIC CONDUCTIVE OVERCOATING ON SAID PHOTOSENSITIVE COATING WHILE MAINTAINING SAID MASKED STRIP, REMOVING SAID FIRST MASK AND MASKING SAID TRANSVERSE GROOVES WITH A SECOND MASK WHILE LEAVING THE RIDGES BETWEEN GROOVES EXPOSED, THEN REMOVING THE METALLIC OVERCOATING AND PHOTOSENSITIVE MATERIAL FROM THE PORTIONS OF SAID ROD WHICH REMAINS EXPOSED, AND THEREAFTER REMOVING THE SECOND MASK FROM SAID TRANSVERSE GROOVES. 